This invention generally relates to drive-train assemblies, and more particularly to a belt-driven drive-train assembly for performing a power conversion.
Many industries require the performance of a power conversion, i.e., the conversion of mechanical power into electrical power. For example, the wind turbine industry is a rapidly growing segment of the electric power generation industry. Wind turbines provide a method for extracting energy from wind and converting the energy into electricity to be supplied either for individual use or into utility power grids. The conversion of wind energy to electrical energy is accomplished by coupling a turbine rotor blade through a drive-train assembly to a power conversion unit, such as an electrical power generator, so that the passage of wind over the turbine rotor blades results in the rotation of a rotor of the power conversion unit.
One known drive-train assembly for a wind turbine includes a main shaft that connects a blade rotor hub of a turbine rotor blade to a low speed input of a gearbox. A generator is connected to a high speed output of the gearbox. The turbine rotor blade drives the low speed shaft of the gearbox, which transforms the torque and speed of the turbine rotor blade to the required torque and speed of the generator. Often the gearbox includes a complex set of planetary gears, which may include sun, planet and ring gears, that provide the means to transmit the torque from the turbine rotor blades to the generator. With time, small metallic particles accumulate within the gearbox as the surfaces of the gears rub together. The accumulation of the metallic particles greatly accelerates the degradation of the entire gear box. Oil sensors, filters in the gear box oil circuitry, and ultrasonic sensors for the detection of frequencies within the gear box indicative of components undergoing rapid wear are known to alleviate these gearbox reliability problems. However, these solutions are sophisticated and expensive.
In addition, drive-train assemblies that utilize gearbox based designs encounter cost and size limitations as the turbine rotor blade diameter is increased beyond current standard lengths of approximately 60 to 70 meters. In particular, the weight and cost of the gearbox is determined by the torque carrying capacity of the low speed input of the gear box. This torque capacity must increase with approximately the cube of the turbine rotor blade diameter, as the rotational speed decreases with the rotor blade diameter to maintain a turbine rotor blade tip speed which is within the allowable noise generation limits. Disadvantageously, the cost and weight of the gear box rapidly becomes prohibitively high as the length of the turbine rotor blade is increased.
Another known drive-train assembly for wind turbines includes a main shaft which connects the turbine rotor blade directly to a large generator. The electrical rotor inside the generator rotates in unison with the turbine rotor blade. These drive-train assemblies also create cost and weight problems. In fact, known direct drive generator drive-train assemblies are nearly twice as heavy as gearbox design drive-train assemblies due to the rapid increase in cost and weight associated with increasing turbine rotor blade diameter. This rapid increase stems from the cubic growth in weight required in response to the slower revolution of the turbine rotor blade. Additionally, direct drive generators necessitate heavy generator frames built to tight tolerances. Disadvantageously, this requirement may be expensive and difficult to manufacture.
Accordingly, it is desirable to provide an improved drive-train assembly for performing a power conversion that is inexpensive, reliable and that provides modularity in design.